The present invention relates to radar electronics, and more particularly, to a method and means for transferring or shifting the radar return signal of a doppler radar from one target being tracked to another. It applies especially to the field of testing or training, where practice firings of a radar-guided missile are directed toward a purposely supplied incoming target or targets.
At the present time, remotely controlled drone aircraft carry one or more airborne targets which are launched from the drone and have a short self-propelled flight period and then a free-flight period during which they are used as practice targets for missiles using doppler radar to home in on the target. As the carrier drone approaches the firing range, the radar of a ground-to-air missile, for example, picks up and tracks the carrier drone with its attached target. The target is launched from the carrier as the missile approaches, soon enough for safe separation at missile impact, but not so soon that the target glide time expires before intercept. After launch of the target, then, the missile is to track and aim at the target alone, while the carrier drone can turn and cruise until another approach and target launch or else return to its base and land for installation of more of the expendable targets.
The missile guidance doppler radar uses a velocity gate to distinguish the intended target from objects at other speeds, but sometimes the velocity gate is not pulled off from the carrier drone to the target when the latter rapidly accelerates away from the drone during target launch. As a result, the fired missile continues training on the drone and can hit it instead of the intended target.
The use of velocity-gate pull-off (VGPO) systems for deceptive countermeasures against doppler radars has been widespread, but such conventional systems would not solve the problem identified above. In such systems the VGPO is followed by an abrupt stop in radar return signal or an abrupt shift in doppler for the purpose of causing the radar to revert to an acquisition or hunting mode. In this mode the radar is likely to re-acquire the drone rather than the target, and in addition would subject the missile system which is being evaluated to unacceptable transients.
The present invention may be called a velocity-gate hand-off (VGHO) system. It is the purpose of the present VGHO invention not to simply pull off the velocity gate from one object, but to hand it off or transfer it smoothly to another object (target).
A further object of this invention is to hand off the velocity gate of a tracking doppler radar from a target carrier vehicle to the target when the target is launched from its carrier, so that a missile guided by the radar will then aim at the target alone and not at the carrier vehicle.
It is another object in such a VGHO device to hand off the velocity gate of a doppler radar guided missile without introducing significant transients in the radar system.